The invention relates to a swim fin, comprising a seat for the foot, the so-called footpocket and a propelling blade, which has a central longitudinal member for supporting and stiffening the blade, substantially extending from the tip portion of the footpocket to the free end edge of the blade, thereby dividing the blade into two half-blades.
Various types of fins are known, which have a central longitudinal blade-stiffening member, designed to limit its resiliency and increase its propulsive force.
These prior art fins may include, on the surfaces of the two half-blades, a plurality of ribs or hollows, particularly axially oriented, for a better water canalization.
In accordance to another prior art fin, each of the two half-blades consists of a plurality of relatively resilient small blades extending outwards from the central longitudinal member. These small blades are spaced, and the gaps between each two small blades are open, and this reduces the capacity of the blade to take on water.
While these prior art fins have blades constructed in such a manner as to operate more effectively as compared with the traditional fins, they do not reach the ideal hydrodynamic behavior.
In certain cases, water is taken on by the fin in an unsatisfactory manner, otherwise it requires an excessively heavy blade, having an excess of moving masses, which require a considerable effort by the user.
Therefore, the present invention has the purpose to improve, by simple and inexpensive arrangements, a fin such as the one described hereinbefore, to achieve a better hydrodynamic behavior, closer to the optimum, and to obtain a greater propulsion with a lower muscular effort of the lower limbs, thereby reducing the risk of cramps. Particularly, a fin is desired which has a much lighter blade as compared with prior art fins, and at the same time an equal or even greater propulsive potential.
The invention achieves the above objects by providing a fin as described hereinbefore, in which the blade has at least one pair of additional rib-like stiffening members or the like, which are relatively rigid but resilient, each of which extends over a half-blade and branches off from the central longitudinal member to the corresponding side edge of the half-blade. The rest of the blade may be at least partly closed by at least one waterproof membrane-like element or the like, which has a higher resiliency than the ribs.
In accordance with a preferred embodiment, which will be described in greater detail with reference to the drawings, each half-blade may include a plurality of ribs branching off from the central longitudinal member. Said ribs may be spaced and the gaps between ribs may be closed at least partly by the above-mentioned waterproof element.
The ribs may be disposed in a substantially parallel arrangement, and oriented towards the free end of the blade. Hence, each of them forms an acute angle with the section of the central longitudinal member included between the rib attachment portion and the free end of the longitudinal member.
Like in other prior art fins, the central longitudinal member may be made of a relatively rigid, preferably thermoplastic material, and its width and/or thickness may decrease toward the free end thereof. Hence, it has a certain stiffness at the footpocked attachment portion and an increasing resiliency toward the free end of the blade.
Advantageously, the central longitudinal member may have, in its thickest portion, i.e. in the footpocket attachment portion, and particularly immediately before the beginning of the bottom side thereof, one or more weakened areas, consisting of inserts, notches or the like, for a local increase of resiliency.
The ribs may be made of a relatively rigid plastic material, particularly of the same thermoplastic material as the central longitudinal member, and are arranged symmetrically with reference to the median longitudinal axis of the blade, i.e. to the central longitudinal member.
On each half-blade a rib may end at and form the corner portion of the half-blade near the free end of the blade.
The ribs which end at the lateral edges of the blade and at the two corner ends may have the same length and/or width and/or thickness, or a different width and/or length and/or thickness.
The gaps between every pair of ribs may be equal or different in width with respect to each other and/or to the ribs, but preferably all have substantially the same width as the ribs.
The closing elements, the membranes or the portions of the closing element between every pair of ribs may be thinner than the ribs, or have the same thickness and extend flush therewith on one or both faces of the blade.
The closing elements, the membranes or the portions of the closing element between every pair of ribs may have the same length as the ribs for an optimal thrust through water.
The gaps between ribs may be closed by a single element, which may be a film, a sheet or the like, extending in such a manner as to cover the whole surface of at least one face of the blade and fastened onto the surface of the ribs by chemical/physical bonding, e.g. welding, gluing, or the like.
In a particular embodiment, both faces of the blade may be covered by a film, a sheet or other similar element.
Alternatively, the gaps between ribs may be closed, at least partly by a plurality of elements in the form of films, sheets or the like, applied and welded along the inner edges of the adjacent ribs, in such a manner as to extend flush with one of the faces of the blade.
As a further alternative, said gaps may be closed, at least partly, by a plurality of resilient filling elements, each interposed between a pair of adjacent ribs, which may have the same thickness as the ribs, so as to extend flush with the two faces of the blade or a lower thickness.
Said resilient closing elements may be made by injecting a filling material into the gaps between adjacent ribs. Alternatively, prefabricated resilient members may be inserted and fastened by chemical/physical bonding on the inner edges of the ribs.
Materials with a good resiliency though with no extensibility may be used as closing materials, e.g. synthetic thermoplastic materials, such as polyethylene, polyurethane, polypropylene, PVC, EVA, PTE, or the like, or one or more layers made of artificial and/or synthetic and/or natural braided, woven or otherwise processed resins.
Alternatively, materials having a good resiliency and a certain extensibility may be used to close the gaps, e.g. thermoset rubber, or the like, to achieve a particular hydrodynamic behavior.
The whole surface of the blade may be closed in a waterproof manner or one or more apertures for water passage may be provided at predetermined locations, designed, for example, to increase the resiliency of these areas and/or to decrease pressure on water.
The ribs may be directly connected to the central longitudinal member, or there may be provided, at least for some of the ribs, higher resiliency connection portions having a hinging effect, preferably disposed next to the longitudinal member.
Particularly, for each rib, the portion having a hinging effect may include, at least for some of the ribs, one or more weakening grooves provided on one or both faces of the rib.
Alternatively, for each rib, the portion having a hinging effect may include, at least for some of the ribs, an elongated aperture which extends on a portion of the rib width. Hence, the rib is connected to the longitudinal member by two highly resilient bridges of material at the ends of the aperture.
As a further alternative, there may be provided, for at least some of the ribs, a plurality of bore-like apertures, or the like. Therefore, each rib is connected to the central longitudinal member by a plurality of bridges of material.
In the footpocket attachment portion, the blade may have two apertures for water passage, one on each side of the footpocket.
Particularly, the blade may have two substantially triangular members, situated on opposite sides with respect to the longitudinal member, consisting each of a relatively rigid plastic frame, which will be described below in greater detail.
These frame-like members may be closed, at least partly, like the gaps between the ribs, or otherwise, e.g. by means of a more rigid closing element, but preferably have each a substantially triangular aperture for water passage.
At the free end portion of the longitudinal member there may be provided a pair of end ribs, preferably having a smaller width and length than the others, which branch off from the longitudinal member and reach the edge of the free end of the blade.
These two ribs may be connected together along the edge of the free end of the blade by a transverse member, in such a manner as to form therewith a substantially triangular element, divided into halves by the end section of the longitudinal member.
This element may be closed like the gaps between the ribs, or in a different manner, or may be at least partly open and have two apertures on opposite sides of the longitudinal member.
The advantages of the present invention are self-evident from the above description and consist in that a novel fin may be provided by simple and inexpensive arrangements, which allows to achieve a better hydrodynamic behavior, closer to the optimum. An increased propulsion can be obtained with a smaller muscular effort of the lower limbs, especially thanks to the fact that the fin of the invention includes a blade which has a highly peculiar structure, whereby it is much lighter than prior art fins. The fin has an in-fluid behavior comparable to that of a plume or a bird""s feather, and has a propulsive capacity equal to or higher than prior art fins.
Further characteristics and improvements of the invention will form the subject of the dependent claims.